package auth

import (
	"context"
	"crypto/hmac"
	"crypto/sha256"
	"encoding/base64"
	"encoding/json"
	"errors"
	"fmt"
	"strings"
	"time"
)

type tokenPayload struct {
	Subject string `json:"sub"`
	Type    string `json:"typ,omitempty"`
	OpenID  string `json:"openid,omitempty"`
	UnionID string `json:"unionid,omitempty"`
	Issued  int64  `json:"iat"`
	Expires int64  `json:"exp"`
}

func signToken(userID string, secret string, ttl time.Duration, now time.Time) (string, int64, error) {
	if ttl <= 0 {
		ttl = 7 * 24 * time.Hour
	}
	return signTypedToken(userID, "access", secret, ttl, now)
}

func signRefreshToken(userID string, secret string, ttl time.Duration, now time.Time) (string, int64, error) {
	if ttl <= 0 {
		ttl = 30 * 24 * time.Hour
	}
	return signTypedToken(userID, "refresh", secret, ttl, now)
}

func signTypedToken(userID string, tokenType string, secret string, ttl time.Duration, now time.Time) (string, int64, error) {
	payload := tokenPayload{
		Subject: userID,
		Type:    tokenType,
		Issued:  now.Unix(),
		Expires: now.Add(ttl).Unix(),
	}
	token, err := signPayload(payload, secret)
	return token, int64(ttl.Seconds()), err
}

func parseToken(ctx context.Context, token string, secret string, now time.Time) (string, bool) {
	if err := ctx.Err(); err != nil {
		return "", false
	}
	parts := strings.Split(strings.TrimSpace(token), ".")
	if len(parts) != 2 {
		return "", false
	}
	expected := signBytes([]byte(parts[0]), secret)
	actual, err := base64.RawURLEncoding.DecodeString(parts[1])
	if err != nil || !hmac.Equal(expected, actual) {
		return "", false
	}
	data, err := base64.RawURLEncoding.DecodeString(parts[0])
	if err != nil {
		return "", false
	}
	var payload tokenPayload
	if err := json.Unmarshal(data, &payload); err != nil {
		return "", false
	}
	if payload.Subject == "" || payload.Expires <= now.Unix() {
		return "", false
	}
	if payload.Type != "" && payload.Type != "access" {
		return "", false
	}
	return payload.Subject, true
}

func signWechatBindingToken(identity WechatIdentity, secret string, ttl time.Duration, now time.Time) (string, int64, error) {
	if ttl <= 0 {
		ttl = 5 * time.Minute
	}
	if strings.TrimSpace(identity.OpenID) == "" {
		return "", 0, fmt.Errorf("%w: wechat identity is incomplete", ErrInvalidCredentials)
	}
	payload := tokenPayload{
		Type:    "wechat_binding",
		OpenID:  strings.TrimSpace(identity.OpenID),
		UnionID: strings.TrimSpace(identity.UnionID),
		Issued:  now.Unix(),
		Expires: now.Add(ttl).Unix(),
	}
	token, err := signPayload(payload, secret)
	return token, int64(ttl.Seconds()), err
}

func parseWechatBindingToken(ctx context.Context, token string, secret string, now time.Time) (WechatIdentity, bool) {
	payload, ok := parsePayload(ctx, token, secret)
	if !ok {
		return WechatIdentity{}, false
	}
	if payload.Type != "wechat_binding" || payload.OpenID == "" || payload.Expires <= now.Unix() {
		return WechatIdentity{}, false
	}
	return WechatIdentity{OpenID: payload.OpenID, UnionID: payload.UnionID}, true
}

func signPayload(payload tokenPayload, secret string) (string, error) {
	data, err := json.Marshal(payload)
	if err != nil {
		return "", err
	}
	encodedPayload := base64.RawURLEncoding.EncodeToString(data)
	signature := signBytes([]byte(encodedPayload), secret)
	return encodedPayload + "." + base64.RawURLEncoding.EncodeToString(signature), nil
}

func parsePayload(ctx context.Context, token string, secret string) (tokenPayload, bool) {
	if err := ctx.Err(); err != nil {
		return tokenPayload{}, false
	}
	parts := strings.Split(strings.TrimSpace(token), ".")
	if len(parts) != 2 {
		return tokenPayload{}, false
	}
	expected := signBytes([]byte(parts[0]), secret)
	actual, err := base64.RawURLEncoding.DecodeString(parts[1])
	if err != nil || !hmac.Equal(expected, actual) {
		return tokenPayload{}, false
	}
	data, err := base64.RawURLEncoding.DecodeString(parts[0])
	if err != nil {
		return tokenPayload{}, false
	}
	var payload tokenPayload
	if err := json.Unmarshal(data, &payload); err != nil {
		return tokenPayload{}, false
	}
	return payload, true
}

func signState(secret string, ttl time.Duration, now time.Time) (string, int64, error) {
	stateID := newID()
	token, expiresIn, err := signToken(stateID, secret, ttl, now)
	if err != nil {
		return "", 0, err
	}
	return token, expiresIn, nil
}

func verifyState(ctx context.Context, state string, secret string, now time.Time) error {
	if strings.TrimSpace(state) == "" {
		return fmt.Errorf("%w: state is required", ErrInvalidCredentials)
	}
	if _, ok := parseToken(ctx, state, secret, now); !ok {
		return fmt.Errorf("%w: state is invalid", ErrInvalidCredentials)
	}
	return nil
}

func hashVerificationCode(code string, target string, secret string) string {
	value := strings.TrimSpace(target) + ":" + strings.TrimSpace(code)
	return base64.RawURLEncoding.EncodeToString(signBytes([]byte(value), secret))
}

func signBytes(data []byte, secret string) []byte {
	secret = strings.TrimSpace(secret)
	if secret == "" {
		secret = "local-dev-change-me"
	}
	mac := hmac.New(sha256.New, []byte(secret))
	_, _ = mac.Write(data)
	return mac.Sum(nil)
}

func bearerToken(header string) (string, bool) {
	header = strings.TrimSpace(header)
	if header == "" {
		return "", false
	}
	parts := strings.Fields(header)
	if len(parts) != 2 || !strings.EqualFold(parts[0], "Bearer") {
		return "", false
	}
	return parts[1], true
}

func normalizeTokenErr(err error) error {
	if err == nil {
		return nil
	}
	if errors.Is(err, ErrInvalidCredentials) {
		return err
	}
	return fmt.Errorf("%w: %v", ErrInvalidCredentials, err)
}